The basic purpose of these studies remains the investigation of renal behavior towards chloride as distinct from sodium. Firstly, the studies are directed towards determining the factors affecting, the stimulus for, the mechanism of, and the structural changes associated with tubular chloride transport, including the processes underlying chloride conservation by the distal nephron. Secondly, they are directed towards elucidating the effects of variation in total body chloride, changes in plasma chloride, dietary chloride intake, and chloride depletion on renal function, extracellular fluid and vascular fluid volume, acid base balance, and renal tubular handling of electrolytes and hydrogen ion. Observations will be made on the effect of variation in plasma chloride, bicarbonate and acid base status on sodium absorption in the renal tubule using balance and micropuncture techniques. Thirdly, serial studies of a rat model of congenital progressive cystic renal disease by functional radiological and anatomical methods will be continued. Experiments will involve manipulation of total body chloride by diet, diuretics, peritoneal dialysis and primary acid base changes. Techniques will include metabolic balance studies, determination of muscle, renal, blood and urinary electrolytes and acid base status, and micropuncture observations on tubular chloride transport.